1. Field of the Invention
The present invention relates to a bilobed fuselage for an aircraft which is intended to be employed for carrying passengers or freight, or both. The invention is more particularly concerned with a bilobed fuselage for a high-capacity transport aircraft.
The invention is also directed to aircraft equipped with a fuselage of this type.
2. Description of the Prior Art
Generally speaking, the design of an aircraft fuselage has to satisfy a large number of criteria. These give rise to compromises between requirements of a functional character and requirements of a structural character so as to result in acceptable weight and minimum production cost. It is readily apparent that this design must also be adapted to aeronautical certification requirements and to market requirements.
An aircraft fuselage normally has the function of carrying a payload in the form of passengers and baggage as well as freight. In regard to the cabin, this implies flexibility in the arrangement of seats and service locations (galleys, toilets, and so on) as well as suitable means for access and evacuation. The compartments provided for freight are usually loaded by passing into the fuselage on only one side. This makes it possible to reduce stopover times since access to passengers is provided on the other side of the fuselage.
In order to build structures of acceptable weight, it is necessary to take into account the pressurization of the cabin, which ensures a comfortable atmosphere during high-altitude flight as well as the total load constituted by the resultant of the forces generated by the flight mission of the aircraft under given atmospheric conditions. For the greater part of the fuselage, the pressure within the interior of the cabin is the predominant load to be taken into account for dimensioning. In this connection, the optimum structure is constituted by a segment of cylindrical fuselage having a substantially circular or practically circular cross section. The difference in pressure prevailing on each side of the shell results in peripheral stress which is counterbalanced by longitudinal members as well as by transverse structures known as frames, and pressure-resistant partition walls or bulkheads.
Production costs may be substantially reduced by making use of parts which already exist in other types of aircraft. Similarly, it is an advantage to develop aircraft having identical subassemblies or subassemblies comprising many common parts since initial production tooling costs may accordingly be amortised over a larger series. Furthermore, it may prove justified to make fuller use of automation owing to the additional reduction in costs which is thus made possible.
In the field of aeronautics, market requirements tend to impose an increase in the number of passengers which can be carried by a single aircraft while at the same time maintaining acceptable external dimensions of the aircraft. The object of this tendency is to limit the congestion of airports and air traffic by reducing the number of flights. A further object is to obtain a direct operating cost (DOC) per passenger which is as low as possible. As a general rule, the cost just mentioned includes a percentage of the initial purchase price, the cost of fuel, costs of operating personnel (crew) and of maintenance. Under these conditions, if additional seats are installed at limited cost, this may appreciably reduce the direct operating cost per seat. Similarly, a large baggage-hold volume which can effectively be employed for freight or other purposes may significantly reduce operating costs owing to the possibilities of additional income which are thus offered.
In order to increase the usable volume of the fuselage without excessively increasing the external dimensions of the aircraft, different cross sections have been studied. Vertical bilobed fuselages or in other words fuselages having two longitudinal lobes placed one above the other and juxtaposed in a horizontal plane have already been built and put into service.
While being relatively compact, this form of construction is nevertheless subject to disadvantages in regard to volume utilization of the fuselage and complicates passenger access to the upper deck, taking into account existing airport facilities. This entails the need to install interior stairways, thus reducing available space as well as the structural efficiency of the aircraft.
It has also been proposed to construct an airplane having a fuselage which is bilobed in the lateral or horizontal direction or in other words which has two longitudinal lobes juxtaposed substantially in a longitudinal vertical plane. This is the case in particular of U.S. Pat. No. 3,405,893 (C. Flamand et al) and U.S. Pat. No. 4,674,712 (Whitener) which describe a bilobed-fuselage airplane, each lobe being limited by a flat longitudinal wall along its intersection with the other lobe. This dividing wall, which is thus vertical in the trim position of the airplane, constitutes a common vertical joint plane. Moreover, the two lobes are surrounded by an air-tight outer shell of oval cross-section which is formed of high-strength metal. In the upper portion reserved for passengers, a few openings of limited number are provided for passing from one lobe to the other.
This bilobed-fuselage airplane constitutes a rather small improvement over conventional aircraft for the following reasons:
the presence of an oval shell of high-strength metal and of a central wall over the greater part of the length of the aircraft result in a weight estimate which is not improved or which is improved only to a very slight extent;
the central wall, which is almost continuous, increases the weight of the aircraft and constitutes a considerable obstacle to the movement of passengers from one side of the aircraft to the other. This is a very serious disadvantage from the point of view of passenger safety in the event of incident or of accident. As a further consequence, service on board the aircraft is also unfavorably affected and the same applies to freight loading conditions since in this case both sides of the fuselage have to be employed in practice for passenger access.
The present invention relates to a different design of aircraft fuselage, the greater part of which has a body which is bilobed in the lateral direction. The object of the invention is in fact to construct a fuselage by means of existing components, the increase in weight of this fuselage being relatively small with respect to the increase in the number of seats of the upper deck and/or with respect to the increase in freight as well as increased flexibility in the distribution of seats.
The invention is also directed to a high-capacity aircraft in which the movement of persons from one side of the aircraft to the other is greatly facilitated in order to comply with aviation safety regulations and to permit entry of passengers through only one side of the fuselage.